The best size for me is 8 x 8 printed on an 11 x 14 sheet of paper which is how I've been printing these for some time now. All are sold ready for framing and mounted and overmatted to 16 x 20 on 4-ply Winchester Bright White.
Just recently I have begun experimenting with a larger size in a small edition at the request of one of my dealers. The dealer's logic is that in their location (Cal) many of their clients have large houses with large walls to fill. They are printed 14 x 14 on a 16 x 20 paper and matted to 20 x 24. Those editions start 200.00 higher than the smaller size, however to date very few have sold. I find that odd as the smaller ones sell quite well, but considering many of the people who know or collect my work expect the 8x8 size, perhaps they just don't accept the addition.
I love some of the larger images, but personally have to confess that I am partial to the smaller size as well - at least for my work. I just seems more intimate.